The primary aim of research in our
laboratory is to understand the relation between the electrical
signals of nerve cells in the retina of the eye and visual
information processing. What are the neural mechanisms which
shape and control these signals? How are these signals related
to visual perception in animals and humans? To search for
answers to these questions, we study the electrical response
of retinal neurons evoked by precisely-controlled light
stimuli. Of late we are using computer-controlled active
matrix LCD panels in some of this work. We are primarily
interested in the retinal mechanisms of color vision, contrast
vision and adaptation.
Our work on adaptation centers on
intracellular recording from single cone photoreceptors
in the turtle retina and the use of a new laser-based technique
to measure changes of the photopigment concentration in
cone photoreceptors in the intact retina. Our work on contrast
vision involves intracellular recording from retinal neurons
and the analysis of extracellular recordings of the impulse
discharge of retinal ganglion cells in the tiger salamander
retina. The aim is to understand how information for visual
contrast (the "gray scale" for vision) is encoded
and transformed across the synapses of the retinal network.
We have already found that ganglion and amacrine cells are
remarkably sensitive to very small steps of contrast and
that much of this sensitivity arises from a great amplification
of the contrast signal impressed at the synapse between
the cone photoreceptors and retinal bipolar cells.
Burkhardt, D.A. (1995). The influence
of center-surround antagonism on light adaptation in cones
in the retina of the turtle. Visual Neuroscience, 12, 877-885.
Burkhardt, D.A. and Fahey, P. Responses
of ganglion cells to contrast steps in the retina of the
light-adapted tiger salamander. Visual Neuroscience, In
press.
Burkhardt, D.A. and Fahey, P. Contrast
enhancement and distributed encoding by bipolar cells in
the retina. Journal of Neurophysiology, In press.
